Abstract
On our planet, aqueous environments such as deep sea or high-altitude aphotic lakes, subject to present or past volcanic activity and active deglaciation, may provide analogues to the aqueous environments found on such planetary bodies as Europa, Titan or Enceladus. We report here methodologies and technologies tested in Laguna Negra, a high altitude lake in the Central Andes, Chile, for exploring and assessing the presence of life within planetary lakes or interior oceans. We adopted a multi-parametric Rapid Ecological Assessment (REA) approach centered around collecting video imagery (by an Underwater Imaging System) and sampling benthic sediments (for sedimentological, biological and geochemical analysis) to depths of 272 m, to complement physico-chemical sampling of the water column and collection of shallow sediments for microbiological analysis (reported in separate publications). This enabled us to classify and assess the apparent status of benthic habitats, based on substrata and environmental characteristics, together with floral and faunal community characteristics and bioturbation artifacts. Videos imagery showed that the lower water column was characterized by a variably intense sestonic flux of particles and debris among which were planktonic organisms such as ostracods, copepods and possibly cladocerans. Sediment analysis revealed at all depths abundant diatom frustules, mainly of an acidophile pennade diatom Pinnularia acidicola, amid vegetal debris likely originating from littoral macrophytes. Video imagery showed that the lakebed was partly covered by microbial mats and depositional matter and harboured an unexpectedly rich assortment of macrofauna, including sponges, tubificid worms, flatworms, bivalves and crustaceans. Various forms of bioturbation were also encountered, some with the animals in the tracks. Most notably, at the deepest site, a previously undescribed faunal feature was evident, apparently formed by a mat-like community of several layers of what appeared to be polychaete tubeworms, possibly of the family Siboglinidae. It is hypothesized that the hydrothermal activity observed in the region may supply the compounds able to support the deep-water microrganisms from which such tubeworms typically gain sustenance. Such processes could be present on other deep and aphotic liquid-water-bearing planetary bodies.
Highlights
Interpretation of images taken by the Hubble Space Telescope would suggest that plumes of water erupt from Jupiter’s icy moon Europa (Roth et al, 2014) and from Enceladus, one of Saturn’s moons (Postberg et al, 2011; Thomas et al, 2016)
Laguna Negra is one of at least 84 closed-basin lakes present in this part of Chile and adjacent Bolivia, most of which are saline in nature (Risacher et al, 2001; Alvial et al, 2008), but the water column of Laguna Negra has been recorded has having a low conductivity (130–139 uS/cm) (EcheverríaVega et al, 2018) indicating that, at least in its upper parts, it is not at all saline
The studies were thought to confirm that Laguna Negra is an oligotrophic, cold water (4◦C) lake, typical of the region (Modenutti et al, 2013)
Summary
Interpretation of images taken by the Hubble Space Telescope would suggest that plumes of water erupt from Jupiter’s icy moon Europa (Roth et al, 2014) and from Enceladus, one of Saturn’s moons (Postberg et al, 2011; Thomas et al, 2016). Complementary work involved the analysis, using a Rapid Ecological Assessment (REA) approach, of video imagery collected from all depths, supplemented by the collection of water-sediment samples from the bottom of the lake for sedimentological, biological and geochemical analysis (Tilot, 2014a) The latter supplemented previous microbiological analysis of bottom sediments using (a) DNA extraction, cloning and sequencing, (b) ammonia oxidizing activity and nitrate and sulfate evolution testing in separate mesocosm experiments, and (c) microarray immunoassays with an immunological Life Detector Chip (LDChip) with a 300-antibody microarray biosensor developed for planetary exploration and environmental monitoring (Parro et al, 2018, 2019). We present the main results of the REA work directed at to a multi-parametric assessment of the lake ecosystem directed at understanding the structure and functioning of the lake ecosystem
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